1. Field of the Invention
The present invention relates to a developing apparatus that uses a non-magnetic mono-component toner. More particularly, the present invention relates to an apparatus in which toner can be added to the developing unit when existing toner in the developing unit is consumed, and a method for adding toner to the developing unit.
2. Description of the Related Art
The life span of a developing unit in a conventional developing apparatus that uses a non-magnetic mono-component developer typically depends on the amount of toner contained in the developing unit and the printing speed. Generally, a developing apparatus contains enough toner to print from 2000 to 3000 sheets. The life span of the components of the developing unit (for example, the developing roller, the developing blade, the supply roller, etc.), however, is longer than this. Therefore, when the toner is depleted, the components must be changed, even though they have a remaining useful lifespan. This provides certain advantages. For example, a manufacturing firm does not have to provide after sales services and a user can print high quality images by replacing the developing unit. However, since environmental waste should be reduced as much as possible, research has been conducted on methods of changing the toner in the developing unit and reusing the developing unit. These methods have typically been used with developing apparatuses that use a dual-component developing agent.
When only toner is replaced in the developing unit, toner having the same cores and external additives as the existing toner is used. A core is a particle including at least resin and colorant and has an average diameter of 3 to 10 μm. The external additives are wax or a charge control agent (CCA), which are not added to the cores. Toner can be produced using a pulverization method in which the raw material is fused and mixed and then pulverized and classified, or using a polymerization method in which a monomer is suspended and emulsified to be polymerized.
Generally, when toners with different compositions are mixed in a developing unit, one toner is charged positively and another toner is charged negatively. Thus, background contamination occurs in a printed image, and the optical density of a solid part of the printed image increases unnecessarily, thereby increasing toner consumption. In some cases, the optical density of the solid part decreases, and consequently, high quality images cannot be regularly produced.
Accordingly, there is a need for a developing apparatus that uses non-magnetic mono-component toner and produces high quality images which can be refilled.